Comments on: Nucleophile attacks Electrophile

By: Pete

Pete — Fri, 19 Jun 2015 13:52:36 +0000

In reply to João Louçano. I'm afraid I disagree. Why would the molecule choose to be bent? It can be sp hybridized and linear, placing the positive charge in a p-orbital on carbon, and making the C-R sigma bond lower in energy since it has more s-character, or it can be sp2 hybridized with the charge in an sp2 orbital. It seems to me there would be a steric AND electronic penalty for the acylium cation to be anything but linear.

By: João Louçano

João Louçano — Thu, 19 Feb 2015 23:58:22 +0000

In reply to Jonathan Minkin.

Hi Jonathan!

You posed a very interesting question. Allow me to contribute to the debate.
The linear resonance structure of the acylium cation is an oxonium cation: the positive charge is localized in the oxygen atom. Oxygen is very electronegative and more electronegative than carbon. Oxonium cations are thus hardly stable (although there are exemples in nature – anthocyanins) and consequently the contribution of this resonance structure to the resonance hydrid should be small.
I would expect the resonance hybride to have a slightly larger angle than the typical 120 degrees for sp2 carbons.

By: Jonathan Minkin

Jonathan Minkin — Tue, 11 Mar 2014 07:29:47 +0000

A big fan of your site.
Just one question about the geometry of the acylium cation intermediate of the friedel crafts acylation reaction. Since one resonance structure is linear (carbon triply bonded to carbon) and one resonance structure is depicted here as ‘bent’ (carbon doubly bonded to carbon) would you expect the resonance hybrid to be linear, bent, or somewhere in between?

By: Gloria

Gloria — Wed, 24 Oct 2012 03:10:52 +0000

Sorry for such a late post on an old topic. Basically I’m a biochem student and google always helps a lot and I fall onto your site quite often, it’s been very helpful so thank you. I’ve read this post and for the life of me can’t stop thinking about the whole “nucleophile attacks electrophile” thing. I know most reactions occur that way, but what about electrophilic substitution/addition if those two things are the same. I know cations such as carbocations don’t generally exist because they’re unstable and only form as a result of some nucleophilic attack, and lately in the last few classes this has been plaguing me because all I do notice is some negative thing attacking a positive thing and I can’t for the life of me think about any exceptions. Then where does electrophilic substitutions fit in all this? Is it that in electrophilic mechanisms, the solvent does something to the molecule so that it becomes a cation first and then nucleophile attacks? Can it be said that electrophilic substitutions are basically the counterpart of nucleophilic substitutions? Then where exactly is the difference? Thanks!

By: The Six Pillars of Organic Chemistry « Master Organic Chemistry

The Six Pillars of Organic Chemistry « Master Organic Chemistry — Wed, 25 Aug 2010 14:09:31 +0000

[…] assist with understanding the driving forces of most reactions in organic chemistry. ”Nucleophile attacks electrophile“, for example, is an extremely simplifying way of looking at chemical reactions, and […]